This invention relates to an image forming apparatus, and in particular, to an image forming apparatus capable of eliminating various kinds of deviation such as distortion and positional deviation in an image formed on a recording sheet.
A copying machine, a printer, a facsimile apparatus, etc. (These are hereinafter referred to as xe2x80x9cimage forming apparatusxe2x80x9d collectively.) are equipped with a function to form an image on a recording sheet.
Further, among image forming apparatus of this kind, there is one wherein a latent image is formed on a photoreceptor by means of a laser beam, the latent image is made a toner image, and this toner image is transferred and fixed to a recording sheet.
Further, in such an image forming apparatus using a laser beam, a polygonal mirror and an fxcex8 lens are used for the scanning of the photoreceptor by the laser beam. Therefore, caused by deviation of the characteristics of the fxcex8 lens from the ideal ones, chromatic aberration of the fxcex8 lens, inclination of the polygonal mirror from the ideal direction, deviation of the polygonal mirror from the ideal position, deviation of the reflection angle characteristic of the polygonal mirror from the ideal one, deviation of the position and inclination of the mounting of the photoreceptor from the ideal values, etc., positional deviation, inclination, and distortion of an image (These are hereinafter referred to as xe2x80x9cdeviationsxe2x80x9d collectively.) are produced, which makes a cause of image degradation.
Further, in a color image forming apparatus of a tandem type for forming a color image, there are a plurality of fxcex8 lenses, polygonal mirrors, laser beams, and photoreceptors in accordance with the number of colors of an image to be formed, and deviations in these components present a registration error in a color image.
For the purpose of correcting the above-mentioned deviations, there exist several methods. The first method is such that exposure beam is detected by a sensor and registration correction is carried out. In this first method, the main object is to adjust the starting position in the main scanning direction. The second method is such that an image on the intermediate transfer member is read by an image sensor and registration correction is carried out. In this second method, the main object is the positional adjustment of a specified portion in the main/sub-scanning directions. The third method is such that an image of a specified pattern is formed, and this image of the specified pattern is read by a scanner. The main object of this third method is inspection.
That is, in any one of the above-mentioned first method to third method, it has never been taken into consideration to carry out the correction of an image distortion and a registration error in a color image for each pixel on the whole surface of the image at an accuracy within one dot.
This invention was made in view of the above-mentioned problem, and it is its object to realize an image forming apparatus capable of carrying out the correction of image distortion and registration error in a color image for each pixel on the whole image surface at a high accuracy.
Further, it is its another object to realize an image forming apparatus capable of carrying out the correction of an image distortion and a registration error in a color image for each pixel on the whole image surface at an accuracy within one dot.
That is, the above-mentioned objects are accomplished by any one of the structures (1) to (6) described below.
(1) An image forming apparatus characterized by comprising an image forming means for forming an image on a recording sheet on the basis of image data and outputting it, an image reading means for reading an image on a document and generating image data, a pattern generating means for generating pattern data for recording a set of test patterns at their respective specified positions on a recording sheet, a positional deviation detecting means for detecting the positional deviation from the position of the proper output at each characteristic point included in the set of test patterns generated by said pattern generating means, and a deviation correcting means for calculating operational values for the correction of each pixel with reference to the respective positional deviations of the characteristic points detected by said positional deviation detecting means and carrying out a processing to eliminate the positional deviation of each pixel in image formation by the use of said operational values, thereby the deviation or the inclination of an image when said image is read by said image reading means, can be corrected.
In this structure, the respective positional deviations of characteristic points, which are included in the set of test patterns from image data obtained by the reading of the recording sheet having the image of said set of test patterns recorded on it, from the positions of their proper output are detected. Then, by the calculation of operational values for the correction of each pixel with reference to the detected positional deviation of the characteristic points and the use of said operational values, a processing to eliminate positional deviation or inclination in image formation is carried out.
As the result of this, it is possible to carry out the correction of image distortion for each pixel of the whole image surface.
(2) An image forming apparatus comprising an image forming means for forming an image on a recording sheet on the basis of image data and outputting it, an image reading means for reading an image on a document and generating image data, a pattern generating means for generating pattern data for recording a set of test patterns at their respective specified positions on a recording sheet, a positional deviation detecting means for detecting the positional deviation from the position of the proper output at each characteristic point included in the set of test patterns generated by said pattern generating means, and a deviation correcting means for calculating operational values for the correction of each pixel with reference to the respective positional deviations of the characteristic points detected by said positional deviation detecting means and carrying out a processing to eliminate the positional deviation of each pixel in image formation by the use of said operational values, which is characterized by the positional deviation to be detected by said positional deviation detecting means and the positional deviation to be corrected by said deviation correcting means being deviations in the main scanning direction and in the sub-scanning direction.
In this structure, the respective positional deviations of characteristic points, which are included in the set of test patterns from image data obtained by the reading of the recording sheet having the image of said set of test patterns recorded on it, from the positions of their proper output are detected. Then, by the calculation of operational values for the correction of each pixel with reference to the detected positional deviation of the characteristic points and the use of said operational values, a processing to eliminate positional deviation or inclination in image formation is carried out.
Further, in this structure, because the positional deviation to be detected and the positional deviation to be corrected are deviations in the main scanning direction and in the sub-scanning direction, it is possible to carry out the correction of image distortion at a high accuracy for each pixel of the whole image surface.
(3) An image forming apparatus comprising an image forming means for forming an image on a recording sheet on the basis of image data and outputting it, an image reading means for reading an image on a document and generating image data, a pattern generating means for generating pattern data for recording a set of test patterns at their respective specified positions on a recording sheet, a positional deviation detecting means for detecting the positional deviation from the position of the proper output at each characteristic point included in the set of test patterns generated by said pattern generating means, and a deviation correcting means for calculating operational values for the correction of each pixel with reference to the respective positional deviations of the characteristic points detected by said positional deviation detecting means and carrying out a processing to eliminate the positional deviation of each pixel in image formation by the use of said operational values, which is characterized by said deviation correcting means comprising a delay means for generating a plurality of clocks having the phase shifted stepwise by 1/n of the period from a basic clock, a selection means for selecting, at the time of correction of a positional deviation in the main scanning direction, a clock in accordance with the amount of the positional deviation, and an output means for outputting an image signal at a specified timing based on said selected clock.
In this structure, it is put into practice that a plurality of delayed clocks having the phase shifted stepwise by 1/n of the period from a basic clock are generated, at the time of correction of a positional deviation in the main scanning direction, a delayed clock is selected in accordance with the amount of the positional deviation, and an image signal is outputted at a specified timing based on said selected clock.
As the result of this, for each pixel of the whole image surface, it is possible to carry out the correction of image distortion and registration error in a color image at a specified position on a recording sheet at a high accuracy with a step smaller than one clock period (1/n of one clock period).
(4) An image forming apparatus comprising an image forming means for forming an image on a recording sheet on the basis of image data and outputting it, an image reading means for reading an image on a document and generating image data, a pattern generating means for generating pattern data for recording a set of test patterns at their respective specified positions on a recording sheet, a positional deviation detecting means for detecting the positional deviation from the position of the proper output at each characteristic point included in the set of test patterns generated by said pattern generating means, and a deviation correcting means for calculating operational values for the correction of each pixel with reference to the respective positional deviations of the characteristic points detected by said positional deviation detecting means and carrying out a processing to eliminate the positional deviation of each pixel in image formation by the use of said operational values, which is characterized by said deviation correcting means comprising a delay means for generating a clock different from a basic clock in the timing by a specified interval, a state detecting means for detecting the delay state of said delay means, that is, to which stage of said delay clock a certain pulse of said basic clock corresponds, a selection means for selecting, with reference to said delay state, at the time of correction of a positional deviation in the main scanning direction, a delayed clock from said delay means in accordance with the amount of the positional deviation, and an output means for outputting an image signal at a specified timing based on said selected delayed clock.
In this structure, it is put into practice that, when a delayed clock different from a basic clock in the timing by a specified interval is generated, the delayed state, that is, to which stage of said delayed clock a certain pulse of said basic clock corresponds, is detected, at the time of correction of a positional deviation in the main scanning direction, a delayed clock is selected in accordance with the amount of the positional deviation with reference to said delayed state, and an image signal is outputted at a specified timing based on said selected clock.
As the result of this, even though the delayed clock generated by the delay means fluctuates owing to various kinds of factor, it is possible to carry out, for each pixel of the whole image surface, the correction of an image distortion and a registration error in a color image at a specified position on a recording sheet at a high accuracy with a step smaller than one clock period.
(5) An image forming apparatus as set forth in any one of the structures (1) to (4), characterized by having a structure which is capable of forming a color image, reading a color image, and detecting positional deviation in a color image, and correcting a registration error for colors composing a color image.
In this structure, an image forming apparatus has a structure which is capable of forming a color image, reading a color image, and detecting positional deviation in a color image, and corrects a registration error for colors composing a color image.
As the result of this, it is possible to carry out, for each pixel in the whole image pixel, the correction of image distortion and colors being out of registration in a color image at a high accuracy.
(6) An image forming apparatus as set forth in any one of the structures (1) to (5), characterized by the aforesaid positional deviation detecting means detecting the corner positions of a recording sheet and applying the information on said corner positions to the detection of positional deviations.
In this structure, it is put into practice that the corner positions of a recording sheet are detected by the positional deviation detecting means, and the information on said corner positions is applied to the detection of positional deviations.
As the result of this, it is possible to carry out, for each pixel in the whole image pixel, the correction of an image distortion and a registration error in a color image at a specified position on a recording sheet at a high accuracy.